Aluminum base alloy



United States Patent 3,136,632 ALUMINUM BASE ALLOY John D. Sprowl,Spokane, Wash, assignor to Kaiser Aluminum & Chemical Corporation,Oakland, Calif, a corporation of Delaware No Drawing. Originalapplication May 26, 1958, Ser. No. 737,485, now Patent No'. 3,055,771,dated Sept. 25, 1962. Divided and this application Nov. 20, 1961, Ser.No. 153,710

2 Claims. (Cl. 75-147) This invention relates to a method for producingcomposite metal articles having a ferrous metal base portion coated withaluminum or aluminum base alloys, the composite article produced therebyand the aluminum base coating alloys. More particularly this inventionrelates to a method for coating a ferrous metal base with aluminum oraluminum alloys which provides a coating characterized by a lustroussmooth appearance free from the presence of stains, the compositearticles produced thereby and the aluminum base coating alloys.

This application is a divisional application of my copending applicationSerial Number 737,485, filed May 26, 1958, now issued as United StatesPatent 3,055,771.

Coatings of aluminum on ferrous metal products are highly desirablesince the composites resulting in effect embody superior propertiesresident in each metal. To the strength and other desirablecharacteristics of the iron or steel core, the aluminum coating adds themore salient properties of resistance to corrosion and oxidation at bothatmospheric and somewhat elevated temperatures, enhanced electricalconductivity, improvement in the brazing of aluminum to steel and a moreattractive appearance.

In the production of aluminum coated ferrous metal articles one of theprimary factors in regard to commercially acceptable results is theappearance of the a coating. A lustrous smooth appearance similar to thecolor and texture of cast aluminum is a desirable characteristic in suchaluminum coatings. When utilizing many aluminizing alloys the coatingsmay display a brown or tan stain, particularly if the ferrous article isquenched in Water while the coating is still molten. Where the aluminumcoated ferrous article is intended for ornamental purposes or for someother reason a stain free surface is desired, many aluminizing alloysmay not be productive of satisfactory results.

In accordance with the prior art, beryllium has been added toaluminizing alloys to provide a clean bath surface and to preventstaining of the coating during air cooling. However, beryllium is veryexpensive and while the amount of beryllium added to the aluminizingalloy may be small, a continual replacement is required to maintainbright coatings. Thus the use of beryllium in aluminizing alloys isexpensive.

Accordingly, it is an object of the present invention to provide amethod of coating ferrous base metal to produce composite articleswherein the coating is characterized by a smooth appearance free oressentially free from any presence of staining.

It is a further object of this invention to provide an aluminum basealloy for coating ferrous base metal articles which provides a coatingin the solid state or ascoated condition eminently suitable forornamental or other purposes due to a lustrous smooth appearance andfreedom from the presence of stains.

It is a still further object of the invention to provide aluminum alloycoated composite articles characterized by a lustrous smooth appearanceand freedom from stains and relatively inexpensive aluminum base alloysfor production thereof wherein conventional methods of hot dip coatingmay be employed.

FF W

. Other objects and advantages of the invention will be apparent fromthe following detailed description thereof.

It has been discovered that the maintenance of a small but effectiveamount of magnesium in a molten coating bath of aluminum results in acoating exhibiting an appearance characterized by freedom from staining.When compared to the appearance of prior art commercially pure aluminumand aluminum alloy coatings, the freedom from staining of the coatingsof the present invention is unique. Examples of prior art aluminum metalbaths for coating ferrous base metal are commercially pure aluminum,aluminum-silicon alloys and an alloy consisting essentially of by weightfrom 1 to 6% silicon, at least one element selected from the groupconsisting of chromium, molybdenum and tungsten in amount from about 0.1to 0.4%, the total not exceeding about 0.5 at least one element selectedfrom the group consisting of boron, titanium, vanadium and zirconium inamount from about 0.02 to about 0.20% boron and titanium, and from about0.1 to about 0.25% vanadium and zirconium, the total of these last namedelements not exceeding about 0.5%, 0.001 to 0.10% sodium, balancesubstantially all aluminum and impurities in normal amounts.

In general it has been found that amounts of magnesium from about 0.05to 0.45% by Weight are productive of satisfactory results wherein theproduction of an attractive relatively smooth stain free coating is theprimary factor with regard to the intended purpose of the compositearticle. However, optimum results in regard to smoothness and freedomfrom staining are realized by amounts of magnesium from about 0.1 to0.2% by 0.05% by weight magnesium do not provide sufiicient resistanceto staining.

Although the addition of magnesium to the aluminum alloy in accordancewith this invention is primarily suited for ornamental purposes due tothe freedom from staining obtained, it was found that there was a lackof any substantial adverse effect upon the ductility of the compositesproduced.

In accordance with this invention, the ferrous articles to be coated arefirst thoroughly cleaned by a suitable method, such as acid pickling, toremove oxide film or scale. They may then be rinsed, dried and immersedin the coating bath with or without the use of a conventional flux. Forlarge sections the use of flux may be used for further cleaning beforeimmersion in the alloy bath. On the other hand, the articles with orwithout pickling, depending on the nature of the surface, may bepretreated by bright annealing in suitable apparatus in an inert orreducing atmosphere and then directly immersed in the molten coatingbath Without exposure to the atmosphere. 7

The bath temperature is maintained suificiently high so that the alloysemployed are completely molten. Of course, the particular bathtemperature depends upon the coating alloy composition and thecomposition and nature of the ferrous article and, in regard to thealloys herein disclosed, temperatures generally of from 1280 to 1375 F.are recommended. j V 7 Since thickness of the Fe-Al interfacial layerincreases with bath temperature,'it is recommended that the lowestoperating temperature consistent with good coating results be used tominimize cracking and spalling' molten bath. The immersion time andalso. the bath temperature may be regulated to produce a compositionsuitable for the intended application. Extending the time of immersiontends to increase the thickness of the FeAl layer and, accordingly, theshortest immersion time consistent with satisfactory coverage is usuallyrecommended.

The improved results obtained by the practice of this invention are morefully illustrated with reference to' the examples below:

Panels of mild steel measuring 4 X 6" X .035 were degreased by furnacebluing then pickled in a 20 HCl solution at 170 F. for from 30 to 120seconds. This was followed by dipping in an aqueous solution of Na SiFplus ZrCl Each specimen was then dipped for from 4 to seconds in amolten bath of aluminum base alloy maintained at 1300 F. Thecompositions of the bath employed are indicated below. The coatedspecimens were then withdrawn and tapped lightly while in countered incontinued operation, 1.7% by weight iron was added to the melt. Theamounts of magnesium as indicated in Table I below were thenincrementally added to the melt and specimens immersed in each alloy.Table V I indicates the appearance of these specimens.

TABLE I Appearance of Aluminized Steel Panels Color Luster Surfacetexture Light tan Very light tan...

Li ht.

Slightly rough.

Do. Do. Smooth.

Do. Do.

Fairly bright do Dull Wrinkled. Very wrinkled.

TABLE II Appearance of Aluminized Steel Panels Percent Color LusterSurface texture Mg by wt.

0.00 Brown spotted Smooth. 0.05. Light- Do. 0.10. Do. 0.20 Do. 0.30 Do.0.40 Slightly wrinkled. 0 50 do Wrinkled. 1.00 do Wrinkled, rough.

Another'aluminum base alloy bath was made up from approximately 10pounds of an aluminum-5% by weight silicon alloy which was melted in aninduction furnace and to which 1.7 by weightiron was added for reasonsDo. Rough and wrinkled;

unsatisfactory.

4 given above. The amounts of magnesium as indicated in Table III belowwere then incrementally added to the melt and specimens immersed in eachalloy. Table III indicated the appearance of these specimens.

TABLE. III

Appearance of Alaminized Steel Panels Percent Mg by wt.

Surface texture Color i Luster Slightly rough.

Rough, wrinkled.

Very rough,

wrinkled.

Another aluminum base alloy bath was made up from approximately 10pounds of an aluminum base alloy consisting essentially of, by weight,2.50% silicon, 0.10% chromium, 0.10% molybdenum, 0.05% titanium, 0.002%sodium, balance substantially all aluminum and impurities in normalamounts, which was melted in an induction furnace and to which 1.7 byweight iron was added for reasons given above. The amounts of magnesiumas indicated in Table IV below were then incrementally added to the meltand specimens immersed in each alloy. Table IV indicates the appearanceof these specimens.

It is readily seen from the results indicated above that the surfaces ofthe aluminized articles employing the principles of this invention weresuperior to those produced outside the teachings of this invention. Morespecifically, it will be noted that those coating baths containingmagnesium in amounts above about 0.45% resulted in coatings which werewrinkled and, accordingly,

Those coating baths containing magnesium contents below about 0.05%resulted in coatings characterized by tan or brown stain and thus werealso unsatisfactory. While some of the samples having magnesium contentswithin the broad range of the invention exhibited slight wrinkling orslight roughness, the coatings produced were satisfactory from anappearance standpoint for many purposes.

As used herein the term aluminurnfv is meant to cover high purityaluminum, commercial purity aluminum and aluminum base alloys.

It will be understood that various changes, omissions and additions maybe made to this invention without departing from the spirit and scopethereof as set forth in the appended claims.

All percentages in the claims are by Weight of the total coating bath.

What is claimed is:

1 An aluminum base alloy for coating ferrous metal wherein the coatedsurface is characterized by smoothness and freedom from staining,consisting essentially of from about I to 6% silicon, at least oneelement selected from the group consisting of. chromium, molybdenum andtungsten in amount from about 0.1 to about 0.4%,

the total not exceeding about 0.5%, at least one element selected fromthe group consisting of boron, titanium, vanadium and zirconium inamount from about 0.02 to about 0.20% boron and titanium, and from about0.1 to about 0.25% vanadium and zirconium, the total of these last namedelements not exceeding about 0.5%, 0.001 to 0.10% sodium, 0.05 to 0.45%magnesium, balance substantially all aluminum and impurities in normalamounts.

2. An aluminum base alloy for coating ferrous metal wherein the coatedsurface is characterized by smoothness and freedom from staining,consisting essentially of 6 about 2.50% silicon, 0.10% chromium, 0.10%molybdenum, 0.05% titanium, 0.002% sodium, 0.1 to 0.2% magnesium,balance substantially all aluminum and impurities in normal amounts.

References Cited in the file of this patent UNITED STATES PATENTS1,932,835 Weber Oct. 31, 1933 2,076,578 Kempf et a1 Apr. 13, 19372,076,579 Kempf et al Apr. 13, 1937 2,908,566 Cron et al Oct. 13, 1959

1. AN ALUMINUM BASE ALLOY FOR COATING FERROUS METAL WHEREIN THE COATEDSURFACE IS CHARACTERIZED BY SMOOTHNESS AND FREEDOM FROM STAINING,CONSISTING ESSENTIALLY OF FROM ABOUT 1 TO 6% SILICON, AT LEAST ONEELEMENT SELECTED FROM THE GROUP CONSISTING OD CHROMIUM, MOLYBDENUM ANDTUNGSTEN IN AMOUNT FROM ABOUT 0.1 TO ABOUT 0.4%, THE TOTAL NOT EXCEEDINGABOUT 0.5%, AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OFBORON, TITANIUM, VANADIUM AND ZIRCONIUM IN AMOUNT FROM ABOUT 0.02 TOABOUT 0.20% BORON AND TITANIUM, AND FROM ABOUT 0.1 TO ABOUT 0.25%VANADIUM AND ZIRCONIUM, THE TOTAL OF THESE LAST NAMED ELEMENS NOTEXCEEDING ABOUT 0.5%, 0.001 TO 0.10% SODIUM, 0.05 TO 0.45% MAGNESIUM,BALANCE SUBSTANTIALLY ALL ALUMINUM AND IMPURITIES IN NORMAL AMOUNTS.